Circuit arrangement for the compensation of a d.-c. bias magnetization of the iron-core of repeaters, or of the reactors arranged between the speaking wires of telephone systems



May 31, 1955 E.. GANITTA 2,709,721

CIRCUIT ARRANGEMENT FOR THE COMPENSATION OF A D-C BIAS MAGNETIZATION OF THE IRON-CORE OF REPEATERS, OR OF THE REACTORS ARRANGED BETWEEN THE SPEAKING WIRES OF TELEPHONE SYSTEMS Filed Nov. 18, 1952 u-i N u u R T U V K, 1G

v w w w r"-} 1"""1 l 1-1 I l I i g; 1 s w "N v u "u INVENTOR E. GAN/TTA ATTORNEY pan CIRQUHT ARRANGEMENT FOR THE CGMPENSA- Til-(3N OF A D.-C. BIAS MAGNETIZATION F THE IRON-CURE 6F REPEATERSi, 0R 9F THE REACTGRS ARRANGED BETWEEN THE S?EAK- ENG WIRES GE TELEPHGNE SYt'sTEMS Eugen Ganitta, Stuttgart, Germany, assignor to International Standard Electric Corporation, New York, N. Y., a corporation of Delaware Application November 18, 1952, Serial No. 321,238

Claims priority, application Germany November 23, 1951 7 tClaims. (Cl. l7-173) T his invention relates to new and useful improvements in telephone systems of the type in which two-conductor speech transmission lines are galvanically separated into two sections by means of interposed repeating coils or condensers, and is more particularly directed to systems in which signalling is effected by means of direct current signals over the speech carrying condoctors or" such lines.

in a known arrangement of one type of speech transmission line, in which a repeating coil is used to separate a section of the line nearer to a calling subscriber from a section remote therefrom, the winding of the repeating coil facing the remote section is divided into two substantially equal parts, one end of each partial winding being connected respectively to one of the conductors of the line and the other ends being connected together through a condenser. The winding of a direct current signal-receiving relay is connected between one terminal of the condenser and ground (or grounded battery) and the relay is then capable of responding to direct current signals impressed on one conductor of the remote section of the line at another point thereon. Such signals may comprise a single direct current pulse or a series of pulses for the purpose of metering a calling subscriber, that is, of registering upon a message register the number of chargeable message-units he is incurring in making his call; and they may occur preferably during the period of conversation.

In a known arrangement of another type of speech transmission line, in which condensers are used to separate the near section of the line from the remote section thereof, the condensers form a part of a highpass filter so dimensioned as to offer a low impedance to speech currents circulating over the line and a high impedance to currents of sub-audio frequencies. A re actor, comprising an inductor and a pair of condensers connected in series, is bridged between the conductors of the remote section of the line and adjacent to the filter; the inductor is provided with two windings, one end of each winding being connected respectively to one of the line conductors and the other ends being connected together through the two condensers in series. The reactor is designed to present a high impedance to the flow of speech currents therethrough. The mid-point of the bridge, that is, the common point between the two condensers, is grounded; the condensers being of similar capacity and the windings of the inductor being substantially balanced, the two halves of the reactor are symmetrical with respect to ground. The winding of a direct current signal-receiving relay is connected in shunt to one of the bridging condensers and the relay is then capable of responding to direct current signals impressed on one conductor of the remote section of the line at another point thereon.

t is a well known requirement of a speech transmission line that the attenuation therein at speech fre- Zfldhfifii Patented May fill, 1955 quencies, resulting from interposing a repeating coil in the line or from the introduction of a bridging reactor, be reduced to a minimum; it is also desirable that the physical size of these elements be as small as possible. To these ends it is necessary to employ magnetic core materials of high efiiciency; however, wound cores of such materials are in general readily saturable by the presence of direct current in their windings.

Both the known arrangements described hereabove are subject to the disadvantage that the direct currents user for operating the signal-receiving relay flow also through a winding of the repeating coil or inductor, respectively, thus reducing the impedance thereof to speech currents and increasing the attenuation in the speech transmission circuit to an undesirable degree, when high eiiiciency magnetic core materials are employed.

The object of the present invention is to overcome this disadvantage and to provide an arrangement whereby the attenuation introduced in a two-conductor speech transmission line by an interposed repeating coil or a bridged inductor is not increased by the flow, for signalling purposes, of direct currents through windings of the repeating coil or inductor.

According to a first embodiment of the invention, a principal feature thereof resides in sub-dividing one winding of a repeating coil, interposed in a speech transmission line to separate it into near and remote sections, into more than two partial windings, and in inter-connecting these partial windings, a plurality of condensers and direct current signal-receiving relay, in such a mannor that a direct current flowing over one conductor of the remote section of the line and through the relay, in order to operate the latter, flows also through a pair of said partial windings, and that the magnetic effects produced upon the core of the repeating coil by said current in each of said partial windings nullify each other.

According to a second embodiment, a principal feature of the invention resides in providing an inductor, forming a part of a reactor bridged between the conductors of a speech transmission line, with more than two windings, and in inter-connecting these windings, a plurality of condensers and a direct current signal-receiving relay, in such a manner that a direct current flowing over one conductor of the line and through the relay, in order to operate the latter, flows also through a pair of said windings, and that the magnetic effects produced upon the core of the inductor by said current in each of said windings nullify each other.

The various features of the invention will become apparent from the following description taken together with the appended drawing, in which:

Fig. 1 shows a known arrangement employing a repeating coil;

Fig.2 shows a known arrangement employing a high pass filter and a bridging reactor;

Fig. 3 shows an arrangement according to the invention employing a repeating coil; and

Fig. 4 shows an arrangement according to the invention employing a bridging reactor.

With reference to Fig. 1, which illustrates a known arrangement, a repeating coil RC separates a two-conductor speech transmission line into a rection c, d, nearer to a calling subscriber and a section a, b, remote therefrom. On the remote side, the conventional split windings I, II, of the repeating coil are joined by a condenser C; and a grounded relay Z, connected to one end of winding II, responds to direct current pulses impressed on conductor b of the remote section of the line from a signalling current source (not shown) at another point thereon. The contacts of relay Z (not shown) may be arranged in any convenient manner to cause, for example, the operation of a subscribers message register. The said direct current pulses, flowing through said winding II, tend to increase the magnetization of the repeating coil core, and thus the attenuation in the speech transmission circuit, to a degree which may be unacceptable.

In Fig. 2 is illustrated another known arrangement. In this case a two-conductor speech transmission line is separated into near and remote sections by condensers C1, C2, C3, C4, which latter, together with an inductor 1C1, constitute a high-pass filter. A reactor, consisting of two condensers C5, C6, and an inductor 1C2 having two windings A, B, is bridged across the conductors a, b, of the remote section of the line, and has its mid-point grounded. A grounded relay Z, connected to one end of winding B, responds to direct current pulses impressed on conductor b at another point on the line. In this case, also, the said direct current pulses, flowing through said windings B, tend to increase the attenuation in the speech transmission circuit which is attributable to the bridging reactor.

Fig. 3 shows one embodiment of the invention, whereby disadvantages inherent in the arrangement of Fig. 1 are overcome. The winding of the repeating coil RC facing the remote section of the line is sub-divided into four substantially equal partial windings III, IV, V, VI, connected in series, with condensers CA1, CA2, separating windings III and IV, V and VI, respectively; the midpoint between windings IV and V is grounded. The relay Z is connected between terminal 3 of winding IV and terminal 7 of winding VI and a metallic circuit may now be traced from ground, terminal d, winding IV, terminal 3, relay Z, terminal '7, winding VI, terminal 8, to line conductor 11. Relay Z will accordingly respond to direct current pulses impressed on said conductor b from a signalling current source (not shown) at another point on the line.

Now, the direction of Winding of the said four partial windings upon the core of the repeating coil RC is such that like currents flowing in the four windings in the direction 1-2, 34, 56, 7-8, respectively, have like magnetic effects on said core, that is, the said windings when connected as shown are all mutually aiding to speech currents flowing between the line conductors a, b. The direct current pulses to which relay Z responds, flow, on the other hand, through the partial windings IV, VI in the direction shown by the arrows, that is, from terminal 4 to terminal 3 of winding IV and from terminal '7 to terminal 8 of winding VI. Owing to the aforesaid direction of winding, the windings IV and VI are mutually opposing to currents flowing in the direction shown by the arrows. Thus, the magnetic effects upon the core of the direct current pulses flowing in the said windings IV and VI annul each other and the undesired magnetiza tion of the core by said pulses is avoided. Consequently, signalling during conversation by means of direct currents, over one conductor of a two-conductor speech transmission line in which a repeating coil is interposed, is no longer an impediment to the use of high-efflciency magnetic core materials in said repeating coil, despite the flow of direct currents through windings thereof.

Another embodiment of the invention, whereby disadvantages inherent in the arrangement of Fig. 2 are overcome, is illustrated in Fig. 4, in which the reactor bridging the remote section of the line consists of two condensers CB1, CB2 and in inductor IC3 having four substantially equal windings P, Q, R, S, and in which the mid-point of the reactor is grounded. The relay Z is connected between terminal 3 of winding Q and terminal 7 of winding S. The four windings are so connected as to be all mutually aiding to speech currents flowing between the conductors a and Z2 and consequently the reactor offers a high impedance to such currents. Direct current pulses for operating relay Z flow from ground, through Winding Q, relay Z and winding S, to the line conductor b in the direction shown by the arrows. The said windings Q and S being mutually opposing to these currents, the magnetic effects thereof upon the core of the inductor ICS annul each other and the attenuation in the speech circuit attributable to the bridging reactor is not increased by said currents. Also, the impedance of the relay Z at speech frequencies can be made high in comparison with impedance of the windings Q, S, and the additional attenuation introduced by the relay is then negligible.

Although in the case described hereabove with reference to Fig. 3, there has been disclosed a preferred method of deriving a direct current signalling circuit from a two-conductor speech transmission line for operating a relay during conversion by current pulses delivered over one conductor of the line, it is equally possible to derive another direct current signalling circuit for operating a second relay by pulses delivered over the other conductor. Relay Z, Fig. 3, connected as shown in dotted lines between terminal 2 of winding III and terminal 6 of winding V, will respond to direct current pulses impressed on conductor a of the line in the same manner as relay Z responds to pulses on conductor b. The two relays Z and Z can then be operated independently and concurrently without interfering with one another or with the speech transmission circuit. It will be evident to one skilled in the art that such a circuit arrangement, in which separate direct: current signalling paths are derived from the two conductors of a speech transmission line can be applied with advantage in certain circumstances, for example, to an inter-office trunk line in a multi-office telephone system, where the well known composite system has been employed hitherto.

It will. also be understood that in the case described hereabove with reference to Fig. 4, it is similarly possible to connect a second relay between terminal 2 of winding P and terminal 6 of Winding R, and to operate it by direct current pulses delivered over conductor a of the line, whereby two independent direct current signalling circuits may be derived from said line.

With reference again to Fig. 3, contacts of a signal transmitting relay or other device can be introduced in the circuit of relay Z, for example, between said relay and terminal 3 of winding IV, whereby direct current signals may be applied to, as well as received from, conductor b of the line. Other circuit combinations can be made for signalling during conversation with direct currents over one or both conductors of a two-conductor speech transmission line, without departing from the scope of the invention.

What is claimed is:

l. A telephone system comprising a two-conductor speech transmission line, an inductor having an even number of windings, a plurality of condensers, a current path bridged between the conductors of said line and including said windings and said condensers connected in series, a connection between ground and an intermediate point in said bridged current path, an inductive device connected between two other intermediate points in said bridged current path to complete a direct current path between ground and one of said conductors including two of said windings, said two windings together being substantially non-inductive to direct currents flowing in said direct current path.

2. A telephone system comprising a two-conductor speech transmission line, an inductor having at least four windings, a pair of condensers, a current path bridged between the conductors of said line and including said windings and said condensers connected in series in the order first winding, first condenser, second and third windings. second condenser, and fourth winding, a connection between ground the interconnecting point of said second and third windings, and a relay connected between the interconnecting point of said first condenser and said second winding and the interconnecting point of said second condenser and said fourth winding, whereby the magnetic effects produced upon the core of said inductor by a direct current flowing between ground and one conductor of said line through said second and fourth windings in series tend to nullify each other.

3. A telephone system comprising a two-conductor speech transmission line having a first and a second section, means for coupling said sections together for the transmission therebetween of speech currents to the exclusion of direct currents and including an inductor having a plurality of windings, a plurality of condensers, a current path bridged between the conductors of one of said sections and including said windings and said condensers connected in series, a connection between ground and an intermediate point in said bridged current path, an inductive device connected between two other intermediate points in said bridged current path to complete a direct current path between ground and one of said conductors including two of said windings, said two windings together being substantially non-inductive to direct currents flowing in said direct current path.

4. A telephone system as claimed in claim 3, in which said means for coupling said sections together comprises a pair of condensers each serially connected between corresponding conductors thereof.

5. A telephone system as claimed in claim 3, in which said means for coupling said sections together comprises a repeating coil.

6. A telephone system comprising a two-conductor speech transmission line having a first and a second section, a repeating coil having a primary winding connected to the conductors of said first section and a secondary winding comprising an even number of partial windings, a plurality of condensers, a current path bridged between the conductors of said second section and including said partial windings and said condensers connected in series,

a connection between, ground and an intermediate point in said bridged current path, and an inductive device connected between two other intermediate points in said bridged current path to complete a direct current path between ground and one of said last-mentioned conductors including two of said partial windings, said two partial windings together being substantially non-inductive to direct currents flowing in said direct current path.

7. A telephone system comprising a two-conductor speech transmission line having a first and a second section, a repeating coil having a primary winding connected to the conductors of said first section and a secondary winding comprising four partial windings, a pair of condensers, a path for speech currents bridged between the conductors of said second section and including said partial windings and said condensers connected in series in the order first partial winding, first condenser, second and third partial windings, second condenser and fourth partial winding, a connection between ground and the interconnecting point of said second and third partial windings, and a relay connected between the interconnecting point of said first condenser and said second partial winding and the interconnecting point of said-second condenser and said fourth partial winding, whereby the magnetic effects produced upon the core of said repeating coil by a direct current flowing between ground and one conductor of said second section through said second and fourth partial windings in series tend to nullify each other.

References Cited in the file of this patent UNITED STATES PATENTS 2,552,780 Hadfield May 15, 1951 

